The present invention relates to condensed aromatic compounds with multiple ring bridging of the general formulae (1), (2), (3), (4) and (5). The invention furthermore relates to the use of the compounds according to the invention in an organic electronic device and to a process for the preparation of the compounds according to the invention. The invention furthermore relates to an electronic device which comprises the compounds according to the invention.
Organic semiconductors are being developed for a number of applications of different types which can be ascribed to the electronics industry in the broadest sense. The structure of organic electroluminescent devices (OLEDs) in which these organic semiconductors are employed as functional materials is described, for example, in U.S. Pat. No. 4,539,507, U.S. Pat. No. 5,151,629, EP 0676461 and WO 98/27136. However, there is still a need for improvement in these devices:    1. In systems in accordance with the prior art, one or more dopants are usually used in a host material in the emitting layer. It would be sensible to have compounds which can be used as pure substance in the emitting layer since this represents a technical simplification in device manufacture.    2. There is still a need for improvement in the lifetime of the organic electroluminescent device in order to employ this for long-lifetime high-quality applications.    3. The thermal stability of many organic compounds which are currently used in organic electroluminescent devices is unsatisfactory, meaning that considerable problems arise both in purification of the material by mass sublimation and in the application of the material by thermal evaporation. This applies, in particular, to compounds which contain styrylamino groups, as are frequently used as blue-emitting compounds.    4. There is also still a need for improvement in the efficiency and operating voltage.
For fluorescent OLEDs, the host materials used in accordance with the prior art are, in particular, condensed aromatic compounds, in particular anthracene or pyrene derivatives, especially for blue-emitting electro-luminescent devices, for example 9, 10-bis(2-naphthyl)anthracene (U.S. Pat. No. 5,935,721). Further anthracene derivatives are disclosed in WO 01/076323, in WO 01/021729, in WO 04/013073, in WO 04/018588, in WO 03/087023 or in WO 04/018587. Host materials based on aryl-substituted pyrenes and chrysenes are disclosed in WO 04/016575. For high-quality applications, it is desirable to have improved host materials available.
Prior art which may be mentioned in the case of blue-emitting compounds is the use of arylvinylamines (for example WO 04/013073, WO 04/016575, WO 04/018587). However, these compounds are thermally unstable and cannot be evaporated without decomposition, which requires high technical complexity for the synthesis and OLED manufacture and thus represents an industrial disadvantage. A further disadvantage is the emission colour of these compounds: whereas dark-blue emission (CIE y coordinates in the range 0.15-0.18) is described in the prior art using these compounds, it has not been possible to reproduce these colour coordinates in simple devices in accordance with the prior art. On the contrary, green-blue emission is obtained here. For high-quality applications, it is therefore necessary to have available improved emitters, particularly with respect to device and sublimation stability and emission colour. The electron-transport compound used in organic electroluminescent devices is usually AlQ3 (aluminium trishydroxyquinolinate) (U.S. Pat. No. 4,539,507). This has a number of disadvantages: it cannot be applied by vapour deposition without leaving a residue since it partially decomposes at the sublimation temperature, which represents a major problem, in particular, for production plants. A further disadvantage is the strong hygroscopicity of AlQ3, as is the low electron mobility, which results in higher voltages and thus in lower power efficiency. In order to avoid short circuits in the display, it would be desirable to increase the layer thickness; this is not possible with AlQ3 owing to the low charge-carrier mobility and the resultant increase in voltage. Furthermore, the inherent colour of AlQ3 (yellow in the solid), which can result in colour shifts, in particular in blue OLEDs, due to reabsorption and weak re-emission, proves to be very unfavourable. It is only possible to produce blue OLEDs here with considerable losses in efficiency and colour location. In spite of the said disadvantages, AlQ3 still represents the best compromise to date for the wide variety of requirements of an electron-transport material in OLEDs.
Thus, there continues to be a demand for improved materials, in particular host materials for fluorescent emitters and triplet emitters, but also emitting compounds, in particular blue-emitting compounds, hole-transport materials and electron-transport materials, which are thermally stable, result in good efficiencies and at the same time in long lifetimes in organic electronic devices, give reproducible results during manufacture and operation of the device, are accessible synthetically simply and in high yields and have high thermal stability.